Obese people tend to perform worse than healthy people at cognitive tasks like planning ahead, a literature review has found, concluding that psychological techniques used to treat anorexics could help obese people too.

According to a review of 38 studies on cognitive function and obesity by researchers from the University of NSW, obese people have a tendency toward “reduced executive function”, meaning planning, goal-oriented behaviour and decision-making.

Obesity may both cause and be caused by the reduced executive function, said review lead author Dr Evelyn Smith, from UNSW’s School of Psychiatry.

“I think it’s a bi-directional relationship. It could be that the cognitive deficiency exacerbates weight gain but once you are obese, there are some aspects of your brain that are affected by the obesity due to inflammation or glucose abnormalities,” she said.

Dr Smith stressed that the review did not conclude that all obese people had poor planning or decision-making skills.

“On average, they have some executive function deficits. People may have deficiencies in all sorts of cognitive processes and this appears to be the most prominent in this group,” she said, adding that the trend was seen across children, teens and adults.

Cognitive remediation therapy, where patients meet specialists regularly to develop new patterns of thinking and planning, has been used to treat anorexia nervosa and could be applied to obese people too, she said.

The studies examined showed an “astoundingly consistent story” of reduced function in the organisational part of obese people’s minds, said
review co-author Professor Lesley Campbell, Senior Principal Research Fellow in Diabetes and Obesity Clinical Studies at the Garvan Institute.

“There seems to be some deficiency in function in that area in paper after paper. The opposite is seen in people who have anorexia, who have strong controlling function,” she said.

“It may be worthwhile to try a similar therapy to help (obese) people instead of just handing out diet sheets and telling them they should exercise,” she said.

The literature review, titled A review of the association between obesity and cognitive function across the lifespan: implications for novel approaches to prevention and treatment, has been published in the journal Obesity Reviews.

However, the review did not demonstrate a causal link between obesity and reduced executive function, said Associate Professor Wendy Brown, Deputy Director of Monash University’s Centre for Obesity Research and Education.

“This study only shows that there is altered cognitive function in the obese. It does not prove that diminished cognition leads to obesity nor does it show that diminished cognition is caused by obesity. It simply recognises a potential association and points to the need for further research such as that being undertaken at Monash University Obesity and Diabetes Institute,” said Dr Brown, who was not involved in the study.

“It would also be interesting to measure the impact of weight loss on this cognitive function.”